1. Field of the Invention
The present invention relates in general to computer mass storage devices, and in more particular to disk array systems for use in computers and electronic equipment, having disk arrays and disk drive control circuitry therein.
2. Description of the Prior Art
Conventionally, when a number of disc or disk drives are connected together in a disk array, there is a method for connection thereof by use of cross-bar switches. In this respect, the small computer system interface (SCSI) is typically used as the input/output (I/O) interface of such disk drives. This system employs a specific scheme for parallel transmission of data in a time division fashion. With this scheme, any accesses to an initiator is simply attained by one-to-one communications over one transmission line path at a time, which suffers from a problem in that disk drives cannot communicate with an increased number of initiators simultaneously. In addition, this scheme strictly requires the use of a limited number of disk drives that can be connected to a single line path, the upper limit of which remains as small as on the order of several tens or less; accordingly, an approach is to employ a method of using associative cross-bar switches enabling a decreased number of controller circuits to control a virtually increased number of disk drives.
To enhance the transaction performance in disk accessing, another approach is also known which attempts to accomplish this by providing a plurality of disk drives. With such a technique, since low-speed operations of seeking mechanisms or the like can be carried out in a parallel manner, it becomes virtually possible to execute a number of processing procedures within a certain time period. Furthermore, it may also be considered that a further increased number of disk drives will be able to be employed due to down-sizing of disk drives in near future. With regard to connection between disk control devices and disk drives, most systems presently employ the interface using SCSI; however, when this interface is applied causing a single interface to attain one-to-one connection for an add-in drive(s), a plurality of interface units should be required raising a difficulty in assembly of these interface units.
Furthermore, the disk drives capable of being connected using one controller is kept decreased in number. To break through this limit, a correspondingly increased number of controllers are to be utilized; alternatively, a branch exchange module is required to compensate for such limitation. This will require the use of an extra controller(s) for control of the branch exchange module, with the result in the essential parts or components being increased in number, which may lead to complexity of dynamic control thereby rendering it difficult.